A variety of methods and apparatus have been used in an effort to kill live pathogens or decompose hazardous compounds within a fluid. One common approach for treating a liquid, known as a pulsed electric field (PEF) process, applies a high frequency pulsed DC voltage to two metal electrodes, which form a treatment chamber between them. The liquid to be treated is passed through the treatment chamber and is in direct physical and electrical contact with the electrodes. The high frequency pulse is intended to prevent electric current from following through the liquid, which can cause unwanted heating.
One disadvantage of the PEF process is that good bacteria kills are often accompanied by a corresponding temperature rise in the liquid being treated This heat can easily damage active components, ingredients or other desirable characteristics of the liquid, such as food nutrients and sensory attributes, including flavors, aromas and colors. If these products are processed they can become unacceptable or their commercial value can be greatly reduced. In the case of biological fluids, living cells may be altered or damaged.
Another disadvantage of the PEF process is the high costs associated with special power supplies that are required to produce the high frequency pulsed DC voltage. Further, the electrodes tend to corrode due to the direct contact between the electrodes and the liquid being treated. Also, since the electrodes are immersed directly in the liquid, the electrodes can be regarded as a major contamination source to the liquid due to oxidation of the electrodes during discharge. The electrodes must therefore be replaced regularly, which further increases maintenance time and costs.
Improved methods and apparatus are desired for treating fluids without decreasing the natural characteristics of the fluid.